In exhaust gas systems, in particular for motor vehicles, metal tubes are conventionally used having a woven jacket, a bellows disposed therein, an agraff-inliner, and optional further equipment. They are preferably used for tube-tube connections. A part of the exhaust gas system, e.g. a tube, is thereby inserted into the metal tube at the input and output sides and welded thereto.
A special variant of this type of connection is a flange connection structure wherein at least one end of the metal tube is provided with a system part which is configured as a connecting flange and which can be connected to the exhaust gas system at an existing point of separation.
To join the connection flange to the metal tube, the flange is conventionally pushed onto a ring provided at one end of the metal tube—without using further components—and welded to the metal tube from the inside.
This procedure precludes welding from the outside in order to guarantee reliable connection of all layers of the tube end.
Disadvantageously, in the MAG welding method (MAG=metal active gas; electric welding method with supplied welding wire which is melted-on) used therefor, welding spatters form which can deposit on the inner side of the metal tube, in particular of the agraff, since complete shielding of the inliner is thereby not possible. This is undesirable, since such material deposits have negative effects on the function of the metal tube, e.g. on its elastic properties, and can damage the engine and/or catalytic converter if they come off during operation.
To prevent these disadvantages, the welding spatters must be removed in a later, costly processing step.
For this reason, the above-described arrangement can be optionally fashioned with an additional intermediate tube disposed inside the metal tube between the connection flange and metal tube to prevent welding spatters.
Towards this end, the flange and the metal tube are pushed onto the intermediate tube and welded thereto from the outside using MAG welding.
This method is disadvantageous in that a second weld seam must be provided which increases production costs and the overall length of the arrangement is increased by approximately the length of the intermediate tube.